The present invention is in the field of applied biotechnology and relates in particular to an economic way of introducing antibodies into a variety of products, especially food and animal feed. The invention further relates to such products.
To fulfil many unmet demands of the society, there is a clear need to provide new products from which consumers may benefit, in particular in the field of food products including animal feed. One of the problems with the presently used consumer products is that if they contain functional compounds, these compounds are not very specific.
For instance, for killing microorganisms in food products the functional compound may be salt or acid. When the concentration of either of these compounds is sufficiently high, they are able to kill microorganisms. However, often the level of salt makes the taste of the product less attractive to the consumer. Moreover, high levels of salt are not recommended by health authorities. The same holds for products that contain considerable amounts of acids or preservatives.
Non-food consumer products such as laundry products may contain compounds that are able to bleach stains, but as they do not specifically recognise stains, considerable amounts of these bleach generating compounds (e.g. percarbonate/TAED) are necessary.
Another example is that some personal hair care products contain compounds that kill the microorganisms involved in dandruff. Also these compounds are not specific and in addition to the causative microorganisms of dandruff they also kill other microorganisms on the skin which are beneficial to the consumer.
Still another example of an unmet demand of the society is the overproduction of manure due to cattle farming. Part of this problem is that the conversion of animal feed into nutrients is not optimal due to the presence of negative compounds like fytic acid.
The above given examples of unmet consumer needs and society seeds can be extended, but it will already be clear that consumer-products and animal feed with compounds which specifically meet the demand of the consumer or society will be of great importance.
The main characteristic of processes in living cells or living species is that they are highly specific. Enzymes just recognise specific substrates and the specificity of antibodies is unsurpassed. Therefore in recent years the industries involved in the manufacturing of (chemical and biotechnological) consumer products or animal feed are increasingly applying biological molecules in order to make their products more specific.
A successful example of this development is the introduction of proteases, lipases, cellulases and amylases in laundry products. These enzymes have a certain specificity and because the production of these enzymes has been improved considerably by recombinant DNA techniques, these microbial enzymes can be produced by microorganisms at costs affordable for consumer products. The introduction of enzymes in detergents has indeed met demands of our society. Over the last decades the energy usage for cleaning of laundry has been reduced with about 50% and the amount of chemicals with about 40%.
In the area of animal feed enzymes can play an important role to reduce the environmental pollution, as has been nicely demonstrated by the application of the enzyme fytase in animal feed. Again this development was possible due to the enormous improvement of the production of fytase by rDNA techniques.
However, often a higher specificity than just recognising a protein or fat is highly desirable to fulfil the unmet demands and therefore the consumer goods and animal feed industry is looking for ways to get specificities in the same order as antibodies have.
In nature microorganisms do not produce antibodies. Although it is well known that by using rDNA technology microorgansims can produce almost any protein, irrespective of its origin, the yield of homologous proteins is much higher than for heterologous proteins. Moreover, expensive purification processes are needed to recover the heterologous protein from its producing cell, since it is not allowed to bring living rDNA organisms into the environment. These two factors, the low production yield and the fact that rDNA organisms have to be separated from the products that they produce have slowed down the introduction of heterologous proteins in consumer products other than in laundry products and some food products. In animal feed only the addition of fytase is a real success up to now.
The present invention relates in particular to introducing certain categories of antibodies into a variety of products, especially food and animal feed.
In WO 94/18330 a method is disclosed for immobilizing a binding protein to the exterior of the cell wall of a microbial host cell, in particular a lower eukaryote, by producing a fusion protein which binds to the anchoring part of a cell wall anchoring protein, thereby ensuring that the binding protein is localized in or at the exterior of the cell wall of the host cell. The binding proteins may ligate or bind to the specific compound to be isolated since they have specific recognition of such compounds or compounds related therewith. Examples of binding proteins mentioned in this reference include antibodies, antibody fragments, combinations of antibody fragments, receptor proteins, etc.
Similarly, WO 94/01567 discloses a method for immobilizing an enzyme to the exterior of the cell wall of a microbial host cell, in particular a lower eukaryote.
Hamers-Casterman et al., Nature (1993) 363:446-448 disclose isolated immunoglobulins from the serum of camelids comprising two heavy polypeptide chains sufficient for the formation of a complete antigen binding site, which immunoglobulins further being devoid of light polypeptide chains.
WO 94/25591 discloses the production of antibodies or functionalised fragments thereof derived from heavy chain immunoglobulins of Camelidae, using transformed lower eukaryote host organisms. The term xe2x80x9cfunctionalized fragmentxe2x80x9d was used for indicating an antibody or fragment thereof to which one or more functional groups, including enzymes and other binding polypeptides, are attached resulting in fusion products of such antibody fragment with another biofunctional molecule. The same definition will be used herein for the present invention.
Spinelli et al., Nature structural biology (1996) 3:752-757 disclose the crystal structure of a llama heavy chain variable domain.
In many processes involving recombinant DNA techniques and culturing or fermenting transformed microorganisms, it is necessary at some stage, for example at the conclusion of the fermentation, to kill the active cells in order to prevent any viable recombinant organisms from being released into the environment.
A conventional way of killing cells is using heat. U.S. Pat. No. 4,601,986 is an example of the use of heat to kill the cells and stop the growth of microorganism cultures. Other conventional ways of killing cells are by lysing the cells, for example by changing the osmotic pressures or by adding enzymes which break down the cell walls or membranes. These techniques are exemplified in U.S. Pat. Nos. 4,299,858, 3,816,260, 3,890,198, and 3,917,510, the disclosures of which are incorporated herein by reference.
In many systems host microorganisms, for example lower eukaryote cells, are difficult to kill. Conventional methods, such as heat, are too severe and may destroy or alter the desired product before the cells are killed. This applies also for the immobilized systems of binding proteins on lower eukaryotes disclosed in WO 94/18330, when the binding protein is an antibody or a functional fragment thereof.
Therefore, there is still a need for stable functional systems involving transformed microorganisms, where the microorganisms are inactivated or killed while the functional activity of the system is substantially maintained. The present invention provides such a stable functional system.
In accordance with the present invention there is provided a product, preferably selected from the group consisting of food products, personal care products, and animal feed products, comprising inactivated recombinant lower eukaryotic cells having at least at their outer surface functionally active antibodies, or functionally active fragments of antibodies.
In a preferred embodiment of the invention, the antibodies or, more preferably, antibody fragments are heavy chain antibodies from Camelidae or the variable domain of these antibodies
The lower eukaryotic cells are substantially inactivated by either one or more physical techniques or chemical treatment, or a combination of physical and chemical treatment. The lower eukaryote cells are preferably inactivated with a factor greater than 106 by physical treatment. Chemical treatment comprises the action of an effective amount of at least one of an antimicrobial agent, for example sorbic acid, benzoic acid, nisin, MB21, or another bacteriocin, and a cell wall degrading enzyme, for example xcex2-(1,3)-glucanase, xcex2-(1,6)-glucanase, chitinase, or a redox enzyme, or a combination of one or more antimicrobial agents and one or more cell wall degrading enzymes.
In another preferred embodiment of the invention, the antibody fragments recognise harmful microorganisms or toxins with a binding constant of  greater than 106, preferably  greater than 107, most preferably  greater than 108.
In another preferred embodiment according to the invention there are provided animal feed products containing killed yeast cells having on their surface one or more functional anti-animal pathogenic microorganisms, for example E. coli, Salmonella, Shigella, and animal viruses. In a preferred embodiment there are provided animal feed products containing inactivated yeast cells having functional anti-E. coli K88 llama antibodies on their surface that protect animals against this pathogenic bacterium.
These and other aspects of the invention will be described in further detail in the description which follows.